Deployment of packet switched telecommunication networks such as Internet protocol Multimedia Subsystem (IMS) networks is on the increase. Many operators are in the process of deploying IMS; initially for voice communication, but soon also for multimedia services. Subscribers of an IMS network may establish and receive voice or video calls. Calls destined for subscribers of an IMS network may originate from a subscriber within the IMS network, or from a telecommunication network outside the IMS network, such as a GSM network, a wireline Public Switched Telephone Network (PSTN), etc.
Call setup requests to a destination subscriber in an IMS network may contain a destination subscriber number, e.g. an E.164 number, to indicate the destination subscriber. The use of E.164 numbers to identify a subscriber is well known since E.164 numbers constitute a convenient method for publicly identifying subscribers in a telecommunication network. Subscribers may migrate from operator to operator, change service provider, and/or change from one network type to another. A subscriber may change for example from a PSTN subscription of a first provider to an IMS subscription of another provider while maintaining the public subscriber number, i.e. E.164 number.
Call setup requests to a destination subscriber in an IMS network must traverse a switching node of the originating network in order to be routed to the destination network. The switching node needs to establish to which destination IMS network the call setup request must be routed. The switching node queries for that purpose a number conversion database node to determine to which network the number of the destination belongs in order to be able to route the call setup request accordingly.
When it has been determined by the number conversion database node that the destination subscriber belongs to an IMS network, the switching node receives network routing information from the number conversion database node relating to the destination IMS network. The call setup request is subsequently routed to the destination IMS network.
Within the destination IMS network the call setup request is first received by an inbound proxy. The inbound proxy queries subscriber information for example in a subscriber database node which then identifies a destination serving node where the destination subscriber is registered. The inbound proxy receives the address of the destination serving node from the subscriber database node and subsequently routes the call setup request to the destination serving node.
The routing of a call setup request towards a destination subscriber of the destination IMS network using E.164 numbers thus causes extensive network traffic load involving the inbound proxy.